Exhaust gas aftertreatment systems for application to automotive internal combustion engines reduce or convert regulated constituents such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) oxides of nitrogen (“NOx”) and, in the case of diesel engines, condensed phase materials (liquids and solids) which constitute particulate matter. With increasingly stringent emission regulation, these exhaust gas aftertreatment systems have become increasingly complex in size, number of components and cost. Existing aftertreatment systems typically utilize individual components each having a discrete function. The components must be arranged in a particular configuration, and with a particular spacing or separation, in order to achieve functional goals. In addition, the introduction of reactants into the exhaust gas may be necessary to promote the reduction and/or oxidation of certain exhaust gas components. The size of the individual components and the packaging within varying vehicle architectures can be a difficult, costly undertaking.
As an example, one NOx abatement technology that is being developed for automotive applications is Selective Catalytic Reduction (“SCR”) in which NOx is reduced with the aid of an ammonia reductant to nitrogen (“N2”) over a catalyst that is typically comprised of zeolite and various base metals. The zeolite/base metal catalyst is disposed on a support structure such as a flow through ceramic or metal monolith. For such applications, urea (typically present in an aqueous solution) or gaseous NH3 is commonly used as the source of the ammonia reductant. The ammonia based reductant is preferably injected far enough upstream of the catalyzed support structure for uniform mixing in the exhaust gas stream. A uniform distribution of reductant with the exhaust gas is necessary to achieve optimal performance of the SCR system. In some cases, various mixing apparatus are installed in the exhaust conduit, upstream of the catalyzed support, to aid in proper mixing of the reductant and the exhaust gas when sufficient flow distance is unavailable. Such mixing apparatus is not particularly desirable in that it is costly, complex and may impact the efficiency of the overall exhaust system.
Additionally, the space required for adequate mixing of a reactant into the exhaust gas stream prevents the placement of the catalyst device in a close mounted configuration in which the catalyzed support is located at or very near to the exhaust outlet of the engine. Such mounting methods may be desirable in that they provide for rapid heat-up and activation, or light-off, of the catalytic device following an engine cold-start, as well as improving the temperature at which the device operates which, with some catalyst compositions, may improve performance.
Accordingly, it is desirable to provide an apparatus that will achieve uniform mixing and distribution of a reactant injected into the exhaust system of an internal combustion engine in an efficient and compact manner.